Trackless electrical driven vehicles of the type disclosed in my U.S. Pat. Nos. 3,914,562 and 4,331,225 utilize a power receiving means for inductively coupling with a conductive power source embedded in the roadway. In order to provide adequate and efficient power transmission from the roadway power source inductor to the power receiving means, the vehicle (and thus its power receiving means) must maintain a position above or laterally aligned with the source within certain limits. Thus, it is necessary to develop a signal on the vehicle that is indicative of the quality of the vehicle's lateral alignment in order for either a driver or an automatic steering system to maintain the necessary positional alignment.
Heretofore, vehicle guidance systems using an embedded conductor that designates a vehicle path have been devised wherein the conductor creates a field of signal energy. Sensors provided on the vehicle are responsive to the signal energy and provide steering signals to maintain the vehicles in line with the conductor. Examples of guidance systems are shown in U.S. Pat. Nos. 4,310,789, 4,215,759 and 4,284,941. In all of the aforesaid patents, the vehicle is powered by means other than an inductively coupled electrical system.
The signal energy from the roadway conductor is typically radiated from a wire in a field that is co-axial with the conductor, and with a field strength that decreases with the radius from the conductor. With vehicles of the inductively coupled type, the shape and field strength of the electromagnetic field above the roadway inductor are very different, with heavier concentrations of flux located at the edges of the steel core of the inductor, and a relatively constant field strength in the region above the broad power conductor. Thus, guidance sensors of types used with embedded conductors would not produce a satisfactory signal versus offset relationship in the presence of the field above a roadway inductor. The present invention provides a solution to the aforesaid problems.